The present invention relates, generally, to a system for coating articles or workpieces and, specifically, for coating metalic articles using electrostatic attraction. The articles to be coated are transported or conveyed through the system by metalic supporting elements such as hooks which hang down from an overhead conveyer. The articles to be coated are grounded via the supporting elements. The articles are first conveyed through a spray booth where they are coated with ionized particles of an uncured material such as plastic resin. The particles are projected in the form of a spray from an electrode unit which charges and ionizes the particles. The particles are attracted to the grounded article and, hence, coat the article. The articles are then conveyed to a curing oven which fixes the particles to the articles to form a permanent coating on the articles. This process is used extensively in the plastic coating industry. The particles are also attracted to the supporting elements so that the supporting elements also become coated. This also means that the particles become fixed to the supporting elements when they are fixed to the article in the curing oven. After a few cycles, the conduction between the articles and the supporting elements ceases to exist. As a result, the quality of the treatment process quickly deteriorates.
In order to maintain an acceptable quality of coating on the articles the supporting elements for the articles must be replaced frequently. This results in a substantial loss of production. The coated supporting elements are either discarded and replaced by new supporting elements or cleaned. In either case, this represents an added cost to the process. At the present time, the preferred form of cleaning consists of burning the coating from the supporting elements. However, this creates two additional problems. The burning requires consumption of energy and creates toxic fumes which must be contained. The equipment for performing both of these tasks and the energy which is consumed therein add considerably to the cost of the coating operation.
Another problem with existing coating systems is that all the particles which are deposited on the carrying elements represent waste. A still further problem arises when the spray is changed to particles having different characteristics such as color. When the spray is changed, the spray booth must be thoroughly cleaned to avoid contaminating the articles with particles from the previous spray. The down time for cleaning the spray booth results in a substantial loss in production. These and other difficulties experienced with the prior art coating systems have been obviated by the present invention.
It is, therefore, a principle object of the invention to provide a system for coating articles by electrostatic attraction in which the particles are removed from the article supporting elements prior to curing of the particles on the article. Another object of the invention is the provision of a supporting element for articles to be coated by electrostatic attraction which enables the supporting elements to be cleaned of the particles while maintaining support of the article.
A further object to the present invention is the provision of a spray booth which limits the amount of deposit of spray particles on the supporting elements of the articles to be coated.
Another object of the present invention is to provide a spray booth for depositing particles on articles to be coated which does not require cleaning when the spray is changed to particles having different characteristics such as color, etc.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.